HIV-negative injection drug users (IDUs) who take antiretroviral therapy (ART) daily can reduce their risk of HIV infection by up to 74 percent, according to a Bangkok study conducted by the U.S. Centers for Disease Control and Prevention, the Thai Ministry of Health, and the Bangkok Metropolitan Administration. Among all the participants given ART as pre-exposure prophylaxis (PrEP), including those who only took their medication 70 percent of the time or less, PrEP reduced the chances of infection by 49 percent.

PrEP cuts the risk of HIV infection in injection drug users in half.

“The CDC trial results prove yet again the power of antiretroviral drugs as HIV prevention and provides another tool to prevent HIV infection in a population at the heart of the HIV epidemic,” says Owen Ryan, amfAR deputy director of public policy. In some regions, including parts of Eastern Europe and Central Asia, 80 percent of new HIV infections are caused by injection drug use. In the U.S., they account for approximately 10 percent. Approximately 40 percent of IDUs in Thailand are HIV positive. “In addition to research on new prevention methods, we need to continue to do the things that we know work well, which is why it is unfortunate that needle and syringe exchange services were not offered to men and women in the Thai study,” says Ryan.

The study involved more than 2,400 Thai IDUs who were all given monthly HIV tests, prevention counseling, and access to risk-reduction strategies including condoms and methadone treatment. The participants receiving ART, not a placebo, were given a once-daily pill containing tenofovir.

“PrEP is an effective but not perfect prevention method and now the work ahead of us relates to implementation,” said Dr. Jonathan Mermin, director of the CDC’s Division of HIV/AIDS Prevention. “We need to know how acceptable PrEP will be among IDU, how we can support adherence in a population that often has chaotic lives, and what’s the best setting for delivery of PrEP.”

Previous studies showed that PrEP cut risk of HIV infection by 44 percent in gay men and other men who have sex with men and by 62 percent in heterosexual men and women. In 2012, the FDA approved using Gilead’s antiretroviral Truvada (which contains tenofovir) as PrEP. The CDC is performing additional research to determine the best PrEP strategies for all adult populations at very high risk of infection. Its interim guidelines for clinicians recommend that they only offer PrEP as part of a comprehensive prevention package.

While the number of Americans using heroin has nearly doubled since 2007, recent studies show that HIV rates among IDUs are declining. A recent CDC report on HIV prevention attributes the decrease directly to safer use of syringes. However, the U.S. federal government currently bans the use of federal funds for programs that employ this prevention strategy and provide clean needles. Similarly, the Thai Ministry of Health would not condone including syringe exchanges in the prevention package provided to participants in the Bangkok study. “CDC does not financially support syringe service programs through our grants due to Congressional legislation,” says Mermin. “I do believe that having access to clean needles is important for people who inject drugs.”